Method of forming fine patterns

ABSTRACT

It is disclosed a method of forming fine patterns comprising: covering a substrate having photoresist patterns with an over-coating agent for forming fine patterns, applying heat treatment to cause thermal shrinkage of the over-coating agent so that the spacing between adjacent photoresist patterns is lessened by the resulting thermal shrinking action, and removing the over-coating agent substantially completely by way of bringing thusly treated substrate into contact with a remover solution for over 60 seconds.

BACKGROUND OF THE INVETNION

[0001] 1. Field of the Invention

[0002] This invention relates to a method of forming fine patterns inthe field of photolithographic technology. More particularly, theinvention relates to a method of forming or defining fine patterns, suchas hole patterns and trench patterns, that can meet today's requirementsfor higher packing densities and smaller sizes of semiconductor devices.

[0003] 2. Description of the Related Art

[0004] In the manufacture of electronic components such as semiconductordevices and liquid-crystal devices, there is employed thephotolithographic technology which, in order to perform a treatment suchas etching on the substrate, first forms a film (photoresist layer) overthe substrate using a so-called radiation-sensitive photoresist which issensitive to activating radiations, then performs exposure of the filmby selective illumination with an activating radiation, performsdevelopment to dissolve away the photoresist layer selectively to forman image pattern (photoresist pattern), and forms a variety of patternsincluding contact providing patterns such as a hole pattern and a trenchpattern using the photoresist pattern as a protective layer (maskpattern).

[0005] With the recent increase in the need for higher packing densitiesand smaller sizes of semiconductor devices, increasing efforts are beingmade to form sufficiently fine-line patterns and submicron-electronicfabrication capable of forming patterns with linewidths of no more than0.20 μm is currently required. As for the activating light raysnecessary in the formation of mask patterns, short-wavelength radiationssuch as KrF, ArF and F₂ excimer laser beams and electron beams areemployed. Further, active R&D efforts are being made to find photoresistmaterials as mask pattern formers that have physical properties adaptedto those short-wavelength radiations.

[0006] In addition to those approaches for realizingsubmicron-electronic fabrication which are based on photoresistmaterials, active R&D efforts are also being made on the basis ofpattern forming method with a view to finding a technology that canprovide higher resolutions than those possessed by photoresistmaterials.

[0007] For example, JP-5-166717A discloses a method of forming finepatterns which comprises the steps of defining patterns(=photoresist-uncovered patterns) into a pattern-forming resist on asubstrate, then coating over entirely the substrate with a mixinggenerating resist that is to be mixed with said pattern-forming resist,baking the assembly to form a mixing layer on both sidewalls and the topof the pattern-forming resist, and removing the non-mixing portions ofsaid mixing generating resist such that the feature size of thephotoresist-uncovered pattern is reduced by an amount comparable to thedimension of said mixing layer. JP-5-241348 discloses a pattern formingmethod comprising the steps of depositing a resin, which becomesinsoluble in the presence of an acid, on a substrate having formedthereon a resist pattern containing an acid generator, heat treating theassembly so that the acid is diffused from the resist pattern into saidresin insoluble in the presence of an acid to form a given thickness ofinsolubilized portion of the resist near the interface between the resinand the resist pattern, and developing the resist to remove the resinportion through which no acid has been diffused, thereby ensuring thatthe feature size of the pattern is reduced by an amount comparable tothe dimension of said given thickness.

[0008] However, in these methods, it is difficult to control thethickness of layers to be formed on the sidewalls of resist patterns. Inaddition, the in-plane heat dependency of wafers is as great as ten-oddnanometers per degree Celsius, so it is extremely difficult to keep thein-plane uniformity of wafers by means of the heater employed in currentfabrication of semiconductor devices and this leads to the problem ofoccurrence of significant variations in pattern dimensions.

[0009] Another approach known to be capable of reducing patterndimensions is by fluidizing resist patterns through heat treatment andthe like. For example, JP-1-307228A discloses a method comprising thesteps of forming a resist pattern on a substrate and applying heattreatment to deform the cross-sectional shape of the resist pattern,thereby defining a fine pattern. In addition, JP-4-364021A discloses amethod comprising the steps of forming a resist pattern and heating itto fluidize the resist pattern, thereby changing the dimensions of itsresist pattern to form or define a fine-line pattern.

[0010] In these methods, the wafer's in-plane heat dependency is only afew nanometers per degree Celsius and is not very problematic. On theother hand, it is difficult to control the resist deformation andfluidizing on account of heat treatment, so it is not easy to provide auniform resist pattern in a wafer's plane.

[0011] An evolved version of those methods is disclosed in JP-7-45510Aand it comprises the steps of forming a resist pattern on a substrate,forming a stopper resin on the substrate to prevent excessive thermalfluidizing of the resist pattern, then applying heat treatment tofluidize the resist so as to change the dimensions of its pattern, andthereafter removing the stopper resin to form or define a fine-linepattern. As the stopper resin, a water-soluble resin, specifically,polyvinyl alcohol is employed singly. However, the use of polyvinylalcohol singly is not highly soluble in water and cannot be readilyremoved completely by washing with water, introducing difficulty informing a pattern of good profile. The pattern formed is not completelysatisfactory in terms of stability over time. In addition, polyvinylalcohol cannot be applied efficiently by coating. Because of these andother problems, the method disclosed in JP-7-45510 has yet to be adoptedcommercially.

[0012] In addition, in forming patterns by utilizing photolithographytechniques, it is required the prevention of the occurrence of defectson the substrate- and the improvement of throughput.

[0013] JP 2001-281886A discloses a method comprising the steps ofcovering a surface of a resist pattern with an acidic film made of aresist pattern size reducing material containing a water-soluble resin,rendering the surface layer of the resist pattern alkali-soluble, thenremoving said surface layer and the acidic film with an alkalinesolution to reduce the feature size of the resist pattern.JP-2002-184673A discloses a method comprising the steps of forming aresist pattern on a substrate, then forming a film containing awater-soluble film forming component on said resist pattern, heattreating said resist pattern and film, and immersing the assembly in anaqueous solution of tetramethylammonium hydroxide, thereby forming afine-line resist pattern without involving a dry etching step. However,both methods are simply directed to reducing the size of resist tracepatterns themselves and therefore are totally different from the presentinvention in object. Further, those publications do not describe orsuggest the effects of reducing the occurrence of defects by way ofadjusting the times of removing step by washing with water.

SUMMARY OF THE INVENTION

[0014] The present invention has been accomplished under thesecircumstances and has as an object providing a method of forming finepatterns on a substrate having photoresist patterns (mask patterns) asit is covered with an over-coating agent. The method has high ability toreduce the occurrence of defects and to improve throughput.

[0015] In order to attain this object, the present invention provides amethod of forming fine patterns comprising: covering a substrate havingphotoresist patterns with an over-coating agent for forming finepatterns, applying heat treatment to cause thermal shrinkage of theover-coating agent so that the spacing between adjacent photoresistpatterns is lessened by the resulting thermal shrinking action, andremoving the over-coating agent substantially completely by way ofbringing thusly treated substrate into contact with a remover solutionfor over 60 seconds.

[0016] In a preferred embodiment, the heat treatment is performed at atemperature that does not cause thermal fluidizing of the photoresistpatterns on the substrate.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The method of preparing the substrate used in the presentinvention having photoresist patterns thereon is not limited to anyparticular type and it can be prepared by conventional methods employedin the fabrication of semiconductor devices, liquid-crystal displaydevices, magnetic heads and microlens arrays. In an exemplary method, aphotoresist composition of chemically amplifiable or other type is spin-or otherwise coated on a substrate such as a silicon wafer and dried toform a photoresist layer, which is illuminated with an activatingradiation such as ultraviolet, deep-ultraviolet or excimer laser lightthrough a desired mask pattern using a reduction-projection exposuresystem or subjected to electron beam photolithography, then heated anddeveloped with a developer such as an alkaline aqueous solution,typically a 1-10 mass % tetramethylammonium hydroxide (TMAH) aqueoussolution, thereby forming a photoresist pattern on the substrate.

[0018] The photoresist composition serving as a material from whichphotoresist patterns are formed is not limited in any particular way andany common photoresist compositions may be employed including those forexposure to i- or g-lines, those for exposure with an excimer laser(e.g. KrF, ArF or F₂) and those for exposure to EB (electron beams).

[0019] [a.] Over-Coating Agent Application Step

[0020] An over-coating agent is applied to cover entirely the saidsubstrate having photoresist patterns (mask patterns) thereon. Afterapplying the over-coating agent, the substrate may optionally bepre-baked at a temperature of 80-100° C. for 30-90 seconds.

[0021] The over-coating agent may be applied by any methods commonlyemployed in the conventional heat flow process. Specifically, an aqueoussolution of the over-coating agent for forming fine patterns is appliedto the substrate by any known application methods including bar coating,roll coating and whirl coating with a spinner.

[0022] The over-coating agent employed in the invention is to coverentirely the substrate having photoresist patterns (mask patterns)thereon, including patterns typified by hole patterns or trenchpatterns, each of these patterns are defined by spacing between adjacentphotoresist patterns (mask patterns). Upon heating, the applied film ofover-coating agent shrinks to increase the width of each of thephotoresist patterns, thereby narrowing or lessening adjacent holepatterns or trench patterns as defined by spacing between thephotoresist patterns and, thereafter, the applied film is removedsubstantially completely to form or define fine featured patterns.

[0023] The phrase “removing the applied film substantially completely”as used herein means that after lessening the spacing between adjacentphotoresist patterns by the heat shrinking action of the appliedover-coating agent, said film is removed in such a way that nosignificant thickness of the over-coating agent will remain at theinterface with the photoresist patterns. Therefore, the presentinvention does not include methods in which a certain thickness of theover-coating agent is left intact near the interface with thephotoresist pattern so that the feature size of the pattern is reducedby an amount corresponding to the residual thickness of the over-coatingagent.

[0024] In the present invention, the over-coating agent is preferablyemployed that contains a water-soluble polymer.

[0025] The water-soluble polymer may be any polymer that can dissolve inwater at room temperature and various types may be employed withoutparticular limitation; preferred examples include acrylic polymers,vinyl polymers, cellulosic derivatives, alkylene glycol polymers, ureapolymers, melamine polymers, epoxy polymers and amide polymers.

[0026] Exemplary acrylic polymers include polymers and copolymers havingmonomeric components, such as acrylic acid, methyl acrylate, methacrylicacid, methyl methacrylate, N,N-dimethylacrylamide,N,N-dimethylaminopropylmethacrylamide,N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetoneacrylamide, N,N-dimethylamlnoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylamlnoethyl acrylate, acryloylmorpholine, etc.

[0027] Exemplary vinyl polymers include polymers and copolymers havingmonomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone,vinyl acetate, etc.

[0028] Exemplary cellulosic derivatives include hydroxypropylmethylcellulose phthalate, hydroxypropylmethyl cellulose acetate phthalate,hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethylcellulose acetate succinate, hydroxypropylmethyl cellulose,hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetatehexahydrophthalate, carboxymethyl cellulose, ethyl cellulose,methylcellulose, etc.

[0029] Exemplary alkylene glycol polymers include addition polymers andcopolymers of ethylene glycol, propylene glycol, etc.

[0030] Exemplary urea polymers include those having methylolurea,dimethylolurea, ethyleneurea, etc. as components.

[0031] Exemplary melamine polymers include those havingmethoxymethylated melamine, methoxymethylated isobutoxymethylatedmelamine, methoxyethylated melamine, etc. as components.

[0032] Among epoxy polymers and amide polymers, those which arewater-soluble may also be employed.

[0033] It is particularly preferred to employ at least one memberselected from the group consisting of alkylene glycol polymers,cellulosic derivatives, vinyl polymers and acrylic polymers. Acrylicpolymers are most preferred since they provide ease in pH adjustment.Copolymers comprising acrylic polymers and water-soluble polymers otherthan acrylic polymers are also preferred since during heat treatment,the efficiency of shrinking the spacing between the adjacent photoresistpatterns (mask patterns) can be increased while maintaining the shape ofthe photoresist pattern. The water-soluble polymers can be employedeither singly or in combination.

[0034] When water-soluble polymers are used as copolymers, theproportions of the components are not limited to any particular values.However, if stability over time is important, the proportion of theacrylic polymer is preferably adjusted to be larger than those of otherbuilding polymers. Other than by using excessive amounts of the acrylicpolymer, better stability over time can also be obtained by addingacidic compounds such as p-toluenesulfonic acid anddodecylbenzenesulfonic acid.

[0035] The over-coating agent for forming fine patterns may additionallycontain water-soluble amines. Preferred ones include amines having pKa(acid dissociation constant) values of 7.5-13 in aqueous solution at 25°C. in view of the prevention of the generation of impurities and pHadjustment. Specific examples include the following: alkanolamines, suchas monoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenedlamlne,1,4-butanediamine, N-ethylethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such astriethylamine, 2-ethyl-hexylamine, dioctylamine, tributylamine,tripropylamine, triallylamine, heptylamine and cyclohexylamine; aromaticamines, such as benzylamine and diphenylamine; and cyclic amines, suchas piperazine, N-methyl-piperazine and hydroxyethylpiperazine. Preferredwater-soluble amines are those having boiling points of 140° C. (760mmHg) and above, as exemplified by monoethanolamine and triethanolamine.

[0036] If the water-soluble amine is to be added, it is preferablyincorporated in an amount of about 0.1-30 mass %, more preferably about2-15 mass %, of the over-coating agent (in terms of solids content). Ifthe water-soluble amine is incorporated in an amount of less than 0.1mass %, the coating fluid may deteriorate over time. If thewater-soluble amine is incorporated in an amount exceeding 30 mass %,the photoresist pattern being formed may deteriorate in shape.

[0037] The over-coating agent for forming fine patterns is adjusted tohave pH values of 2-3 by the addition of the water-soluble amine. Theremay be cases where the over-coating agent for forming fine patterns isapplied to the substrate having metallic layers easily corroded by anacid, the pH values may be adjusted to 3-5.

[0038] For such purposes as reducing the dimensions of patterns andcontrolling the occurrence of defects, the over-coating agent forforming fine patterns may further optionally contain non-amine based,water-soluble organic solvents.

[0039] As such non-amine based, water-soluble organic solvents, anynon-amine based organic solvents that can mix with water may be employedand they may be exemplified by the following: sulfoxides, such asdimethyl sulfoxide; sulfones, such as dimethylsulfone, diethylsulfone,bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamine and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobuthyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobuthyl ether, propylene glycol, propylene glycolmonomethyl ether, glycerol, 1,2-butylene glycol, 1,3-butylene glycol and2,3-butylene glycol. Among those mentioned above, polyhydric alcoholsand their derivatives are preferred for the purposes of reducing thedimensions of patterns and controlling the occurrence of defects andglycerol is particularly preferred. The non-amine based, water-solubleorganic solvents may be used either singly or in combination.

[0040] If the non-amine based, water-soluble organic solvent is to beadded, it is preferably incorporated in an amount of about 0.1-30 mass%, more preferably about 0.5-15 mass %, of the water-soluble polymer. Ifthe non-amine based, water-soluble organic solvent is incorporated in anamount of less than 0.1 mass %, its defect reducing effect tends todecrease. Beyond 30 mass %, a mixing layer is liable to form at theinterface with the photoresist pattern.

[0041] In addition, the over-coating agent may optionally contain asurfactant for attaining special effects such as coating uniformity andwafer's in-plane uniformity.

[0042] The surfactant is preferably employed that, when added to thewater-soluble polymer, exhibits certain characteristics such as highsolubility, non-formation of a suspension and miscibility with thepolymer component. By using surfactants that satisfy thesecharacteristics, the occurrence of defects can be effectively controlledthat is considered to be pertinent to microforming upon coating theover-coating agent.

[0043] From the points above, surfactants in the invention arepreferably employed at least the one selected among N-alkylpyrrolidones,quaternary ammonium salts and phosphate esters of polyoxyethylene.

[0044] N-alkylpyrrolidones as surfactant are preferably represented bythe following general formula (I):

[0045] where R₁ is an alkyl group having at least 6 carbon atoms.

[0046] Specific examples of N-alkylpyrrolidones as surfactant includeN-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone,N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone andN-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone(“SURFADONE LP 100” of ISP Inc.) is preferably used.

[0047] Quaternary ammonium salts as surfactant are preferablyrepresented by the following general formula (II):

[0048] where R₂, R₃, R₄ and R₅ are each independently an alkyl group ora hydroxyalkyl group (provided that at least one of them is an alkyl orhydroxyalkyl group having not less than 6 carbon atoms); X⁻ is ahydroxide ion or a halogenide ion.

[0049] Specific examples of quaternary ammonium salts as surfactantinclude dodecyltrimethylammonium hydroxide, tridecyltrimethylammoniumhydroxide, tetradecyltrimethylammonium hydroxide,pentadecyltrimethylammonium hydroxide, hexadecyltrimethylammoniumhydroxide, heptadecyltrimethylammonlum hydroxide andoctadecyltrimethylammonium hydroxide. Among these,hexadecyltrimethylammonium hydroxide is preferably used.

[0050] Phosphate esters of polyoxyethylene are preferably represented bythe following general formula (III):

[0051] where R₆ is an alkyl or alkylaryl group having 1-10 carbon atoms;R₇ is a hydrogen atom or (CH₂CH₂O)R₆ (where R₆ is as defined above); nis an integer of 1-20.

[0052] To mention specific examples, phosphate esters of polyoxyethylenethat can be used as surfactants are commercially available under tradenames “PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo SeiyakuCo., Ltd.

[0053] If the surfactant is to be added, it is preferably incorporatedin an amount of about 0.1-10 mass %, more preferably about 0.2-2 mass %,of the over-coating agent (in terms of solids content). By adopting theamount as described above ranges, it may effectively prevent thevariations in the percent shrinkage of patterns, potentially dependingon the wafer's in-plane uniformity which is caused by the deteriorationof coating property, and also prevent the occurrence of defects that areconsidered to have cause-and-effect relations with microfoaming on theapplied film that generates as the coating conditions are worsened.

[0054] The over-coating agent of the invention for forming fine patternsis preferably used as an aqueous solution at a concentration of 3-50mass %, more preferably at 5-30 mass %. If the concentration of theaqueous solution is less than 3 mass %, poor coverage of the substratemay result. If the concentration of the aqueous solution exceeds 50 mass%, there is no appreciable improvement in the intended effect thatjustifies the increased concentration and the solution cannot be handledefficiently.

[0055] As already mentioned, the over-coating agent in the invention forforming fine patterns is usually employed as an aqueous solution usingwater as the solvent. A mixed solvent system comprising water and analcoholic solvent may also be employed. Exemplary alcoholic solventsinclude methyl alcohol, ethyl alcohol, propyl alcohol, isopropylalcohol, glycerol, ethylene glycol, propylene glycol, 1,2-butyleneglycol, 1,3-buthylene glycol and 2,3-butylene glycol, etc. Thesealcoholic solvents are mixed with water in amounts not exceeding about30 mass %.

[0056] [b.] Heat Treatment (Thermal Shrinkage) Step

[0057] In the next step, heat treatment is performed to cause thermalshrinkage of the film of the over-coating agent. Under the resultingforce of thermal shrinkage of the film, the dimensions of thephotoresist pattern in contact with the film will increase by an amountequivalent to the thermal shrinkage of the film and, as the result, thephotoresist pattern widens and accordingly the spacing between adjacentphotoresist patterns lessens. The spacing between adjacent photoresistpatterns determines the diameter or width of the pattern elements to befinally obtained, so the decrease in the spacing between adjacentphotoresist patterns contributes to reducing the diameter of eachelement of a hole pattern or the width of each element of a trenchpattern, eventually leading to the definition of a pattern with smallerfeature sizes.

[0058] The heating temperature is not limited to any particular value aslong as it is high enough to cause thermal shrinkage of the film of theover-coating agent and form or define a fine pattern. Heating ispreferably done at a temperature that will not cause thermal fluidizingof the photoresist pattern. The temperature that will not cause thermalfluidizing of the photoresist pattern is such a temperature that when asubstrate on which the photoresist pattern has been formed but no filmof the over-coating agent has been formed is heated, the photoresistpattern will not experience any dimensional changes. Performing a heattreatment under such temperature conditions is very effective forvarious reasons, e.g. a fine-line pattern of good profile can be formedmore efficiently and the duty ratio in the plane of a wafer, or thedependency on the spacing between photoresist patterns in the plane of awafer, can be reduced. Considering the softening points of a variety ofphotoresist compositions employed in current photolithographictechniques, the preferred heat treatment is usually performed within atemperature range of about 80-160° C. for 30-90 seconds, provided thatthe temperature is not high enough to cause thermal fluidizing of thephotoresist.

[0059] The thickness of the film of the over-coating agent for theformation of fine-line patterns is preferably just comparable to theheight of the photoresist pattern or high enough to cover it.

[0060] [c.] Over-Coating Agent Removal Step

[0061] In the subsequent step, the remaining film of the over-coatingagent on the patterns is removed substantially completely by bringingthusly treated substrate into contact with a remover solution for over60 seconds, and preferably 70 seconds or over. By adjusting the contacttime of the substrate with the remover solution to be over 60 seconds,it is extremely effective in reducing the occurrence of defects on thesubstrate without lowering throughput. If the contact time is 60 secondor less, defects occur on the substrate and the yields be lowered. Theupper time of the contact is not specifically limited, however, it ispreferred 300 seconds or less in view of the reduction of the occurrenceof defects and the improvement of throughput, etc. The method of thecontact may be employed such as a puddle method, a dipping method, ashower method, a spray method, etc., but not limited thereto.

[0062] The remover solution is suitably used a water-based solvent, andmore preferably pure water. Prior to the removal step, rinsing mayoptionally be performed with an aqueous solution of alkali (e.g.tetramethylammonium hydroxide (TMAH) or choline). The over-coating agentin the present invention is easy to remove by washing with water and itcan be completely removed from the substrate and the photoresistpattern. The present invention can effectively reduce the occurrence ofdefects entirely. Specifically, among varieties of defects, the presentinvention is extremely effective in reducing the occurrence of thedefects that are filled in the portions of holes and spacing areas.

[0063] As a result, each pattern on the substrate has a smaller featuresize because each pattern is defined by the narrowed spacing between theadjacent widened photoresist patterns.

[0064] The fine-line pattern thus formed using the over-coating agent ofthe present invention has a pattern size smaller than the resolutionlimit attainable by the conventional methods. In addition, it has a goodenough profile and physical properties that can fully satisfy thecharacteristics required of semiconductor devices.

[0065] Steps [a.]-[c.] may be repeated several times. By repeating steps[a.]-[c.] several times, the photoresist trace patterns (mask patterns)can be progressively widened. Furthermore, the use of the over-coatingagent for forming fine patterns containing a water-soluble polymerallows the over-coating agent be completely removed with water everytime in repeating the removal step plural times. Therefore, the presentinvention offers the advantage that even in the case of using asubstrate having thick-film photoresist patterns, fine-line patterns ofgood profile can be formed on the substrate without causing patterndistortion or deformation.

[0066] The technical field of the present invention is the semiconductorindustry, etc., but it is not limited thereto.

EXAMPLES

[0067] The following examples are provided for further illustrating thepresent invention but are in no way to be taken as limiting. Unlessotherwise noted, all amounts of ingredients are expressed in mass %.

Example 1

[0068] A copolymer including polyacrylate (PAA) and polyvinylpyrrolidone(PVP) [2 g: PAA/PVP=2:1 (polymerization ratio)], triethanolamine (0.18g) and a polyoxyethyelene phosphate ester surfactant (0.02 g; “PLYSURFA210G”, product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved inwater (52 g) to prepare an over-coating agent.

[0069] A substrate (8-inch diameter) was whirl coated with apositive-acting photoresist TDUR-PO36PM (product of Tokyo Ohka KogyoCo., Ltd.) and baked at 80° C. for 90 seconds to form a photoresistlayer in a thickness of 0.48 μm.

[0070] The photoresist layer was exposed with an exposure unit (CanonEPA-3000EX3, product of Canon Inc.), subjected to heat treatment at 120°C. for 90 seconds and developed with an aqueous solution of 2.38 mass %TMAH (tetramethylammonium hydroxide) to form photoresist patterns whichdefined hole patterns with an each diameter of 178.9 nm (i.e., thespacing between the photoresist patterns, or the initial hole dimension,was 178.9 nm).

[0071] The previously prepared over-coating agent was applied onto thesubstrate including hole patterns and subjected to heat treatment at116° C. for 60 seconds, thereby reducing the each size of the holepatterns. Subsequently, the substrate, while being kept whirling at 1500rpm, was brought into contact with pure water by dropping it on thesubstrate for 120 seconds to remove the over-coating agent. The eachdiameter of the hole patterns was reduced to 150.8 nm. The state ofdefects on the substrate was observed with KLA (product of KLA Tencor),however, few defects were occurred on the entire substrate.

Example 2

[0072] The same procedure as described in Example 1 was repeated, exceptthat the substrate was brought into contact with pure water by droppingit on the substrate for 90 seconds. Each diameter of the hole patternswas narrowed to 158.3 nm, and few defects were occurred on the entiresubstrate

Comparative Example 1

[0073] The same procedure as described in Example 1 was repeated, exceptthat the substrate was brought into contact with pure water by droppingit on the substrate for 60 seconds. Each diameter of the hole patternswas narrowed to 158.8 nm. However, the observation with KLA revealed theoccurrence of defects on the order of 10-20 in numbers on the substrate.

[0074] As described above in detail, the present invention provide amethod for forming fine patterns, by which advantages obtained ofreducing the occurrence of defects and improving throughput.

What is claimed is:
 1. A method of forming fine patterns comprising:covering a substrate having photoresist patterns with an over-coatingagent for forming fine patterns, applying heat treatment to causethermal shrinkage of the over-coating agent so that the spacing betweenadjacent photoresist patterns is lessened by the resulting thermalshrinking action-, and removing the over-coating agent substantiallycompletely by way of bringing thusly treated substrate into contact witha remover solution for over 60 seconds.
 2. The method of forming finepatterns according to claim 1, wherein the over-coating agent contains awater-soluble polymer.
 3. The method of forming fine patterns accordingto claim 2, wherein the water-soluble polymer is at least one memberselected from the group consisting of alkylene glycolic polymers,cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers,epoxy polymers, melamine polymers and amide polymers.
 4. The method offorming fine patterns according to claim 1, wherein the over-coatingagent is an aqueous solution having a solids content of 3-50 mass %. 5.The method of forming fine patterns according to claim 1, wherein theheat treatment is performed at a temperature that does not cause thermalfluidizing of the photoresist patterns on the substrate.